Concerning neonatal anatomy, the Eustachian valve is best described by which of the following?
A. A flap of tissue at the junction of the IVC and the right atrium
B. A confluence of the right and left hepatic veins
C. A connection of the posterior sinuses to the middle ear
D. A throttle body connection for a 1983 Buick Regal
E. The anti-back flow connector in most pediatric IV tubing
The answer is A.
The Eustachian valve is a flap of tissue at the junction of the IVC and the right atrium. It functions to help direct the higher-velocity stream of blood from the umbilical vein preferentially across the foramen ovale and into the left atrium. The lower-velocity stream of blood in the IVC (from the abdominal organs and lower extremities of the fetus) crosses the tricuspid valve and is ejected by the right ventricle. This flow of various blood streams allows the most oxygenated blood from umbilical vein to bypass the right side of heart and be preferentially shunted to the head and neck vessels.